Gas turbine rotors in gas turbine engines are formed of one or more disks, each with a plurality of blades attached. When operating in a high temperature environment the blades often require air cooling which involves passing air through the blade and out small openings in the blade.
High speed turbine rotors also experience high centrifugal forces. Any portion of the disk which is continuous around the hoop is considered live load since it contributes to resisting the centrifugal force. Any other structure not forming this hoop is considered dead load which increases the forces, but does not contribute to strength. It is desirable to minimize such dead load.
Some design arrangements have included openings or holes through the disks for the purpose of conveying cooling air to the blades. Such openings within the disk are in a high stressed area and act as stress raisers increasing the stress concentrations in the area of the holes.
Conventional blade to disk attachments, such as a fir tree connection, involve a lap construction where the attachment load is up to three times the airfoil dead load. Reduction of the dead load of the attachment scheme would provide reduced rotor weight and increased rotor speed capability.
Other disks have hoop structure on the disk at a location extremely close to the blades. In a high temperature environment this portion of the disk also experiences high temperatures. Such an arrangement may be counterproductive since the high temperature causes expansion of the outer portion of the disk resulting in high thermal stresses which exceed any contribution to strength which this apparent live load has.
The attachment of the blade to the disk must be secure and inspectable. In particular, all edges of any bond should be inspectable to avoid undetected cracks which may propagate during operation. Furthermore, each individual blade is preferably replaceable in the event of damage to a single blade during operation.